The mechanism of chromosome condensation remains virtually unknown. The goal of this proposal is to decipher the action of the condensin, a protein complex most responsible for mitotic chromosome compaction, by combining biochemical, EM/AFM-structural, and single molecule analysis of DNA chromatin acted upon by the purified condensin complexes. Aims: (1) To apply single molecule techniques of optical and magnetic tweezing of DNA to test binding and path reconfiguration by the SMC proteins, the condensin, and condensin regulator complex. (2) To use electron and atomic force microscopy to probe the ultrastructure of condensin-bound DNA. (3) To find and purify the T. thermophila condensin for comparative biochemistry and single molecule experiments. By combining measured condensation forces and fold compaction exerted by the condensin, with EM and AFM structural information, a better description of chromosome condensation promoted by the condensin complex could result. While at first glance seemingly unrelated, Aim (3) will provide a separate condensin from a distantly related organism, and provide valuable comparative molecular analyses from an organinsm also highly amenable to genetic cytological analysis.